NORTHAMPTON — Residents and visitors to the city without a vehicle of their own may soon have access to two additional Zipcars.

Mayor David J. Narkewicz announced Friday he hopes to have the car-sharing service Zipcar provide two cars in the downtown Northampton area for use by its members.

Narkewicz said in a statement released by his office Friday that studies suggest two Zipcars could replace up to 30 privately owned vehicles.

“Zipcar is a cost-effective solution to help us reduce traffic congestion, free up more parking spaces for shoppers, workers, and visitors, and make urban living more convenient,” Narkewicz said in his statement.

Narkewicz added in a telephone interview Friday evening that, if approved, the new cars would complement the existing six-car Zipcar fleet now available on the Smith College campus.

That program began with two cars in August 2006 and increased based on growing demand, Narkewicz said. The popularity of the program at Smith led Zipcar to consider expanding in Northampton.

Narkewicz said based on the expansion of Zipcar membership beyond the Smith College community — the mayor himself is a member — it makes sense to expand in an area where demand is high.

Narkewicz said Zipcar programs are usually centered in larger metropolitan areas where vehicle ownership can be both inconvenient and expensive.

If approved, the cars would be located in two spaces at the E. John Gare Parking Garage. Narkewicz said the spaces would be provided at no cost to Zipcar to them, although under state law a lease agreement with the company is needed even without payment.

“We believe the benefits justify the allocation of these two parking spaces and will be presenting data to the Transportation & Parking Commission and City Council to support this policy decision,” Narkewicz said in an email.

He said the plan would be similar to the accommodations made for electric car charging stations around the city.

Approval for the cars would start with a recommendation from the city’s Transportation and Parking Commission and the necessary ordinance and lease approval for the parking spaces would come from the City Council.

Narkewicz said he expects the Transportation and Parking Commission to take up the issue at 4 p.m. Tuesday in the City Council chambers.

According to its website, Zipcar offers access to the shared cars to members who pay a $25 non-refundable application fee, followed by a $50 per year membership fee. Rates for using the cars start at $8.50 per hour or $69 per day.

The plans include gasoline, insurance and up to 180 miles per day, with extra per-mile charges applied if a driver exceeds those miles, according to Zipcar.